Stethoscopes are used in clinical medicine to listen to heart sounds, lung sounds, and to measure blood pressure through the detection of vascular sounds. In all these applications a single acoustic pickup is sealed to a hose that conveys the information to both ears of a listener simultaneously.
Previous attempts have been made to improve the quality of the transmission of heart sounds, not only through electronic amplification, but also through processing of the heart sound. These attempts have included fairly simple acoustic delays by the use of longer tubing on one channel as is illustrated in U.S. Pat. Nos. 1,817,489; to W. B. Jones, 2,209,164; to W. J. Kerr, and 3,790,711 to Ojima et al. The latter patent also discloses the use of a woofer and tweeter speaker in connection with acoustic delays in tubing.
A very elaborate instrument with complex electronic storage for providing a slowed-down version of an original sound is disclosed in H. V. Katz U.S. Pat. No. 4,528,689. If two sound sensing elements are employed for heart sounds, as in the above identified patent to Kerr, the resulting phase differences in the pickup can cause degradation of the quality of the perceived heart sounds.
Cardiac examination relies extensively on auscultation, that is, the art of listening to heart sounds. As part of a physical examination, the examiner listens to heart sounds, extra sounds, and murmurs such as noises produced by turbulent blood flow. This information conventionally is relayed from the patient's chest to the examiner's ears through one or two stethoscope tubes and presented simultaneously to both ears. Using this method, an average examiner can discriminate a minimum interval between separate sounds of about 40 milliseconds. That is, any two sounds separated by less than 40 milliseconds appear to be a single sound.
The stethoscope disclosed herein provides the ability to differentiate between sounds separated by less than about 40 milliseconds and gives improved clarity and definition to transmitted heart sounds.